Internal combustion engines comprising a turbocharger or a supercharger have an exhaust manifold in which the exhaust lines of the cylinders are grouped in the internal combustion engine. The turbine of the supercharger is provided in the exhaust-gas discharge system. Impulse supercharging at low loads and/or low speeds may increase the turbine rotational speed which can fall during idle operation and/or low load.
One solution to increase turbine rotational speed is to group the cylinders to form the exhaust manifold. This limits the number of turbines and increases the frequency of the pulses that supply each turbine. In another solution a twin-flow turbine may be used such that the rotor is supplied by two adjacent twin exhaust volutes. Further a variable nozzle turbine wherein the nozzle vanes are attached to an axially movable wall to adjust the width of the inlet passageway may be used to optimize gas flow to the rotor.
Some of the problems recognized by the inventors with such set-ups come when running near idle or low load. Grouped cylinders should be set for specific engine types or the pressure fluctuations in the exhaust lines may attenuate one another. The tangential speed of the exhaust gases at the inlet of the rotor may vary greatly with the supply pressures of the two volutes in a twin-flow turbine. The nozzle vanes in a variable nozzle turbine can become jammed or experience reduced movement over their lifetime. Further, leakage of gases from the low pressure side of the nozzle vanes may occur.
One solution relates to a supercharged internal combustion engine having at least one cylinder head with at least two cylinders comprising each cylinder has at least one outlet opening for discharging the exhaust gases out of the cylinder via an exhaust-gas discharge system, and each outlet opening is adjoined by an exhaust line wherein at least two cylinders are configured in such a way as to form two groups with in each case at least one cylinder and the exhaust lines of the cylinders of each cylinder group merge in each case to form an overall exhaust line such that an exhaust manifold is formed. Further the two overall exhaust lines are connected to a two-channel turbine which comprises a rotor which is mounted on a rotatable shaft in a turbine housing such that in each case one overall exhaust line is connected to one of the two inlet openings of the two-cannel turbine and the two channels are separated from one another as far as the rotor by means of a wall such that the streams of the two channels are conducted separate from one another to the rotor. The two-channel turbine comprises a first group of adjustable guide blades at the rotor end of the first channel and a second group of adjustable guide blades at the rotor end of the second channel. In this way it is possible to optimize the configuration of the cylinders to decrease attenuation in the exhaust lines and reduce the potential issues with the nozzle vanes.
Another solution involves a method for operating a supercharged internal combustion engine including a turbine wherein a first group of adjustable guide blades is provided at a rotor side end of a first channel and a second group of adjustable guide blades is provided at a rotor side end of a second channel. This method may reduce variations in the tangential speed of the exhaust gases at the inlet of the rotor.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.